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Papers by Aristides Zdetsis

Journal of Chemical Physics, Mar 1, 1984

Journal of Nuclear Materials

We have developed and implemented on several DEC-5000 work stations, a parallel algorithm suitabl... more We have developed and implemented on several DEC-5000 work stations, a parallel algorithm suitable for distributed concurrent processing, using the Parallel Virtual Machine (PVM). We have used the “regular crowd” structure, in which crowd computations are performed through concurrent processes which are identical. Contrary to the ring structure in which succesive time steps are evolved from one processor to the next, crowd conputations are performed in different groups of space steps. As a basis for the Molecular Dynamics (MD) algorithm, we have taken the MD code of Biswas and Hamann, written in Fortran-77.

In the Frontiers of Computational Science, 2005

Le Journal de Physique Colloques, 1981

Springer Proceedings in Physics, 1988

HOMO–LUMO and optical gaps of (CdSe)n nanocrystals appear to have controversial magnitudes and si... more HOMO–LUMO and optical gaps of (CdSe)n nanocrystals appear to have controversial magnitudes and size dependence, which we have rationalized.

The Journal of Chemical Physics, 2004

Polyethyleneimine is a very interesting polymer, not only for its extensive use in biological app... more Polyethyleneimine is a very interesting polymer, not only for its extensive use in biological applications, but also for its crystal structure as a double-stranded helix in the anhydrous state. In order to elucidate the electronic bulk properties of the crystalline (or linear) polyethyleneimine built from ethylenediamine molecules in anhydrous conditions, we performed ab initio density functional theory calculations on water-free molecular crystal structures. The resulting polymer is a semiconductor with a small band gap: Eg=0.40 eV.

Chemical Physics, 1979

... of distant the origin 1 in set (z1, X-,, x3) 1 FC matrix parameters neighbors 4 4 2 4 1 4..J3... more ... of distant the origin 1 in set (z1, X-,, x3) 1 FC matrix parameters neighbors 4 4 2 4 1 4..J3 4 (4,4,4) ~( ss pppa ss fi a 2 L.,J~ 12 [5] (0,1,1) 11 o -5 -o ~ ry 3 4,/11 12 [19] ( 4, 4, 4) fi ~ ss 0 0 z VV /1 4 4~J1~ 6 [29] (0.0.2) fiE 1f o OOO ~ o O i 5 4~Ji~ 12 [37] (4,4,4) fA o, 0 6 ~ yp 6 24 [49 ...

arXiv: Mesoscale and Nanoscale Physics, 2016

We study the optical properties of hydrogen passivated silicon, germanium and mixed Ge/Si core/sh... more We study the optical properties of hydrogen passivated silicon, germanium and mixed Ge/Si core/shell quantum dots (QDs) using high accuracy Density Functional Theory (DFT) and time-dependent DFT (TDFT). We employ the hybrid DFT functional of Becke, Lee, Yang and Parr (B3LYP) in combination with good quality basis sets. As we have shown in our previous work, this combination is an accurate and computationally efficient way for such calculations. The mixed quantum dots, as would be expected, are more versatile and offer more possibilities for band gap engineering, with gap values (electronic and optical) between those of the corresponding Si and Ge dots. Our results support the quantum confinement theory for all three types of QDs.

Solid State Communications, Sep 1, 1978

ABSTRACT

Springer eBooks, 1985

In previous work1,2, we have obtained an understanding of the role of hydrogen in amorphous silic... more In previous work1,2, we have obtained an understanding of the role of hydrogen in amorphous silicon (a-Si) performing first principles calculations of the electronic and transport properties of a-Si:H using the coherent potential approximation (CPA).

In contrast to alternant nanographenes (NGRs), in non-alternant NGRs no “sublattice structure” ca... more In contrast to alternant nanographenes (NGRs), in non-alternant NGRs no “sublattice structure” can be defined associated with significant conceptual and computational simplifications. This leads to some fundamental differences between the two. We uncover here the broken electron-hole symmetry in non-alternant NGRs as one fundamental difference closely related to distorted Dirac points (cones) and their diradical open-shell character. We also show by higher level calculations beyond common DFT that the alternant series of peri-acenes (bisanthene, peri-tetracene, peri-pentacene, … etc.), contrary to opposite reports in the literature, have clearly closed singlet ground states, in contrast to their non-alternant isomers based on Stone-Wales (SW) defects. This is experimentally supported by sub-molecularly resolved STM images. The misconceptions in the literature are due to insufficient correlation. For non-alternant NGRs/GNRs with antiaromatic rings the driving force for open-shell sta...